#include <iostream>

// GLEW
#define GLEW_STATIC
#include <GL/glew.h>

// GLFW
#include <GLFW/glfw3.h>

#if defined(__linux__)
   #define LINUX
#elif defined(_WIN32)
	#define WINDOWS
#elif defined(__APPLE__)
   #define MAC
#endif

#define FULLSCREEN false

using namespace std;

void key_callback(GLFWwindow* window, int key, int scancode, int action, int mode);

GLint compileVertexShader(const GLchar**);
GLint compileFragmentShader(const GLchar**);

GLint linkShaderProgram(initializer_list<GLint>);

const GLuint WIDTH = 800, HEIGHT = 600;

// Shaders
const GLchar* vertexShaderSource = "#version 330 core\n"
   "layout (location = 0) in vec3 position;\n"
   "void main()\n"
   "{\n"
   "gl_Position = vec4(position.x, position.y, position.z, 1.0);\n"
   "}\0";
const GLchar* fragmentShaderSource = "#version 330 core\n"
   "out vec4 color;\n"
   "void main()\n"
   "{\n"
   "color = vec4(1.0f, 0.5f, 0.2f, 1.0f);\n"
   "}\n\0";

int main(int argc, char* argv[]) {
   cout << "Starting OpenGL game..." << endl;

   cout << "Starting GLFW context, OpenGL 3.3" << endl;
   // Init GLFW
   glfwInit();

   // Set all the required options for GLFW
   glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
   glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
   glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);
   glfwWindowHint(GLFW_RESIZABLE, GL_FALSE);

   #ifdef MAC // required in OSX
      glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE);
   #endif

   // Create a GLFWwindow object that we can use for GLFW's functions
   GLFWmonitor* monitor = FULLSCREEN ? glfwGetPrimaryMonitor() : nullptr;
   
   GLFWwindow* window = glfwCreateWindow(WIDTH, HEIGHT, "LearnOpenGL", monitor, nullptr);
   glfwMakeContextCurrent(window);
   if (window == NULL) {
      cout << "Failed to create GLFW window" << endl;
      glfwTerminate();
      return EXIT_FAILURE;
   }

   // Set the required callback functions
   glfwSetKeyCallback(window, key_callback);

   // Set this to true so GLEW knows to use a modern approach to retrieving function pointers and extensions
   glewExperimental = GL_TRUE;
   // Initialize GLEW to setup the OpenGL Function pointers
   if (glewInit() != GLEW_OK) {
      cout << "Failed to initialize GLEW" << endl;
      return EXIT_FAILURE;
   }    

   // Define the viewport dimensions
   int width, height;
   glfwGetFramebufferSize(window, &width, &height);
   glViewport(0, 0, width, height);

   GLint vertexShader = compileVertexShader(&vertexShaderSource);
   GLint fragmentShader = compileFragmentShader(&fragmentShaderSource);

   GLint shaderProgram = linkShaderProgram({vertexShader, fragmentShader});

   glDeleteShader(vertexShader);
   glDeleteShader(fragmentShader);

   // Set up vertex data (and buffer(s)) and attribute pointers
   //GLfloat vertices[] = {
   //  // First triangle
   //   0.5f,  0.5f,  // Top Right
   //   0.5f, -0.5f,  // Bottom Right
   //  -0.5f,  0.5f,  // Top Left 
   //  // Second triangle
   //   0.5f, -0.5f,  // Bottom Right
   //  -0.5f, -0.5f,  // Bottom Left
   //  -0.5f,  0.5f   // Top Left
   //};
   GLfloat vertices[] = {
       0.5f,  0.5f, 0.0f,  // Top Right
       0.5f, -0.5f, 0.0f,  // Bottom Right
      -0.5f,  0.5f, 0.0f,  // Top Left 
       0.5f, -0.5f, 0.0f,  // Bottom Right
      -0.5f, -0.5f, 0.0f,  // Bottom Left
      -0.5f,  0.5f, 0.0f   // Top Left 
   };
   GLuint indices[] = {  // Note that we start from 0!
      0, 1, 3,  // First Triangle
      1, 2, 3   // Second Triangle
   };
   GLuint VBO, VAO, EBO;
   glGenVertexArrays(1, &VAO);
   glGenBuffers(1, &VBO);
   //glGenBuffers(1, &EBO);
   // Bind the Vertex Array Object first, then bind and set vertex buffer(s) and attribute pointer(s).
   glBindVertexArray(VAO);

   glBindBuffer(GL_ARRAY_BUFFER, VBO);
   glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);

   //glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, EBO);
   //glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(indices), indices, GL_STATIC_DRAW);

   glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 3*sizeof(GLfloat), (GLvoid*)0);
   glEnableVertexAttribArray(0);

   glBindBuffer(GL_ARRAY_BUFFER, 0); // Note that this is allowed, the call to glVertexAttribPointer registered VBO as the currently bound vertex buffer object so afterwards we can safely unbind

   glBindVertexArray(0); // Unbind VAO (it's always a good thing to unbind any buffer/array to prevent strange bugs), remember: do NOT unbind the EBO, keep it bound to this VAO

   // Uncommenting this call will result in wireframe polygons.
   //glPolygonMode(GL_FRONT_AND_BACK, GL_LINE);

   // Game loop
   while (!glfwWindowShouldClose(window)) {
      // Check if any events have been activiated (key pressed, mouse moved etc.) and call corresponding response functions
      glfwPollEvents();

      // Render
      // Clear the colorbuffer
      glClearColor(0.2f, 0.3f, 0.3f, 1.0f);
      glClear(GL_COLOR_BUFFER_BIT);

      // Draw our first triangle
      glUseProgram(shaderProgram);
      glBindVertexArray(VAO);
      glDrawArrays(GL_TRIANGLES, 0, 6);
      //glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, 0);
      glBindVertexArray(0);

      // Swap the screen buffers
      glfwSwapBuffers(window);
   }

   // Properly de-allocate all resources once they've outlived their purpose
   glDeleteVertexArrays(1, &VAO);
   glDeleteBuffers(1, &VBO);
   //glDeleteBuffers(1, &EBO);

   glfwTerminate();
   return EXIT_SUCCESS;
}

// Is called whenever a key is pressed/released via GLFW
void key_callback(GLFWwindow* window, int key, int scancode, int action, int mode) {
   std::cout << key << std::endl;
   if (key == GLFW_KEY_ESCAPE && action == GLFW_PRESS)
      glfwSetWindowShouldClose(window, GL_TRUE);
}

GLint compileVertexShader(const GLchar** shaderSource) {
   GLint vertexShader = glCreateShader(GL_VERTEX_SHADER);
   glShaderSource(vertexShader, 1, shaderSource, NULL);
   glCompileShader(vertexShader);

   // Check for compile time errors
   GLint success;
   GLchar infoLog[512];
   glGetShaderiv(vertexShader, GL_COMPILE_STATUS, &success);
   if (!success) {
      glGetShaderInfoLog(vertexShader, 512, NULL, infoLog);
      cout << "ERROR::SHADER::VERTEX::COMPILATION_FAILED" << endl << infoLog << endl;
   }

   return vertexShader;
}

GLint compileFragmentShader(const GLchar** shaderSource) {
   GLint fragmentShader = glCreateShader(GL_FRAGMENT_SHADER);
   glShaderSource(fragmentShader, 1, shaderSource, NULL);
   glCompileShader(fragmentShader);

   // Check for compile time errors
   GLint success;
   GLchar infoLog[512];
   glGetShaderiv(fragmentShader, GL_COMPILE_STATUS, &success);
   if (!success) {
      glGetShaderInfoLog(fragmentShader, 512, NULL, infoLog);
      cout << "ERROR::SHADER::FRAGMENT::COMPILATION_FAILED\n" << infoLog << endl;
   }

   return fragmentShader;
}

GLint linkShaderProgram(initializer_list<GLint> shaders) {
   GLint shaderProgram = glCreateProgram();

   for (auto shader : shaders) {
      glAttachShader(shaderProgram, shader);
   }

   glLinkProgram(shaderProgram);

   // Check for linking errors
   GLint success;
   GLchar infoLog[512];
   glGetProgramiv(shaderProgram, GL_LINK_STATUS, &success);
   if (!success) {
      glGetProgramInfoLog(shaderProgram, 512, NULL, infoLog);
      cout << "ERROR::SHADER::PROGRAM::LINKING_FAILED\n" << infoLog << endl;
   }

   return shaderProgram;
}